March 31, 2009
One of Google Earth's speed features also has the benefit of enabling the application's use when Internet is not available. The key is the Google Earth cache file which stores imagery and other data locally on your hard drive. This speeds up your experience even when you have broadband Internet, but it also is the secret to offline GE use.
By using the GE cache, you can still use most of Google Earth's features while on an African Safari, while driving your car, while boating offshore, or just camping on a mountain. This includes the aerial/satellite imagery, the 3D terrain, and more. And, the iPhone Google Earthapp has this feature as well. If you anticipate taking your computer (or iPhone) somewhere where you won't have an Internet connection, you can still use GE. Or you can use it for doing a demonstration somewhere without an Internet connection. You will need to do a little preparation first.
First, go to the menu item Tools->Options and select the "Cache" tab. You will not need to change the memory cache for viewing the cache (there is a trick for storing the cache with this setting - see below). The memory cache is set automatically based on your system's memory. You can make the disk cache size as large as 2000 MB (i.e. 2 Gigabytes). This will give you more data to work with. Then, you need to move to the area you want data for and zoom into that area. The most recent things you have looked at will be what's in your cache. It's important you zoom to the closest view you think you'll use. Turn on other layers for information you want cached (for example, 'Terrain', 'Roads' and 'Borders' - the more you select, the faster the cache wil fill). Also, make sure you save any KML files you might want to use in files on the same computer.
The more data you cache, the sooner the cache will fill, so be cautious. If you're going on a long trip, cache in high resolution imagery just the areas where you plan to use GE for close viewing. Avoid turning other layers if you only need imagery. It can be a pain to move around and capture an area of imagery at full high resolution and load up your cache properly. FreeGeographyTools has written some nice tutorials for some free tools for loading your GE cache in a more automated fashion - see here, here, here, and here. There is also a way you can save the cache files to extend the amount of area you can store (see this forum thread).